In a plain-paper copying machine, toner images applied to the surface of paper or other recording medium are fixated by application of heat and pressure. In certain plain-paper copying machines fixation is accomplished by passing the image-bearing recording medium between a hot thermal fixation roll and a pressure roll. When this type of thermal fixation device is used the toner material is directly contacted by a roll surface and a portion of the toner usually becomes adhered to the roll surface. On material may be redeposited on the recording medium resulting in undesirable offset images, stains, or smears; or in severe cases the recording medium may stick to the adhered toner material on the roll and become wrapped around the roll. To counter these problems, materials having good release properties such as silicone rubber or polytetrafluoroethylene are often used for the roll surfaces. Although improving performance of the thermal fixation devices, use of silicone rubber or polytetrafluoroethylene roll surfaces alone does not eliminate the problem. Toner pick-up by the rolls can be controlled by coating the surface of at least one of the rolls with a liquid release agent, such as a silicone oil. It is important that the release liquid be applied uniformly and in precise quantities to the surface of the roll. Too little liquid or non-uniform surface coverage, will not prevent the toner from being picked up from the paper and deposited on the roll. On the other hand, excessive quantities of the release liquid may cause silicone rubber roll surfaces to swell and wrinkle, thus producing copies of unacceptable quality.
Various devices are known in the art for applying liquid release agent to one of the rolls of the fuser system, such as described in U.S. Pat. No. 3,831,553 and European Patent Publication 479564. However, the feature these systems have in common is the provision of a reservoir for holding a quantity of liquid release agent and an oil permeation control layer which is interposed between the reservoir and the roll of the fuser system for controlling the amount of oil which is transferred on to the roll of the fuser system. Various materials are known as the oil permeation control layer, such as porous polytetrafluoroethylene film as disclosed in Japanese Patent Specification No. 62-178992.
British published patent application 2242431 discloses a sintered porous polytetrafluoroethylene structure used as a filter in industrial filtration. The porous polytetrafluoroethylene material is produced by fusing particles of polytetrafluoroethylene such as to form a porous integral network of interconnected particles. The disclosure of this patent specification is incorporated herein.
British published patent application 2261400 (International Patent Publication W093/08512) discloses the use of such sintered porous polytetrafluoroethylene (PTFE) material as an oil transfer component in a copying machine and particularly as an oil permeation control layer to control the amount of release agent applied to the roll in the fuser system. Patent publication EP0174474 (Sumitomo) shows a release oil applicator which comprises a porous body formed of PTFE held in a housing. The PTFE body is saturated with silicone oil and may be formed with various cross-sections.
U.S. Pat. No. 4,336,766 (Maher) shows the use of a compound wick assembly formed from a relatively thick layer of Nomex felt and a relatively thin layer thereof. The thick layer acts as a feeder to convey oil to the thinner layer.
The function of the oil reservoir is to hold quantities of liquid release agent for application to the roll of the fuser system. The reservoir may be pre-loaded with a predetermined quantity of release oil. This is referred to as an "oil-filled device", and is generally discarded once the supply of liquid release agent is used up. Alternatively, the device may be an "oil-fed" device which is supplied with liquid release agent on a continuous basis from a supply device. In both cases, the reservoir has to hold a finite quantity of liquid release agent and should have the ability to supply the liquid release agent at a suitable rate via the oil permeation control layer to the surface of the roll in the fuser system. However, it may be difficult to combine these properties in a single material. For example, a reservoir material having a high void volume and thus a high porosity which enables it to hold relatively large quantities of liquid release agent, may have a relatively low resistance to flow of the liquid release agent, leading to over-supply of release agent. This may be obviated by the presence of the permeation control layer, which controls the rate of delivery of release agent to the roll.
Whilst the sintered porous PTFE material referred to in GB2261400 has good properties as regards oil permeation control and toner wiping from the roll of the fuser system, it has certain drawbacks particularly when the material is to be used as a continuous thin web of sheet material. A continuous web is supplied wound around a feed spool and the web is slowly advanced past the fuser system roll onto a take-up spool during operation. The thin web has a tendency to tear unless care is taken in handling it. Also, webs of good strength tend to have lower porosities so that the oil retention capacity is limited.
It is an object of the present invention to provide an oil transfer component which mitigates the problems associated with known reservoir materials.